how to fix P0420 code in BMW 3 Series G20/G21 (2019-2024)

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is on a level surface and secure it with wheel chocks.
• Disconnect the negative battery terminal to prevent any electrical issues.

2. Inspect and Replace Oxygen Sensors

1. Remove the upstream and downstream oxygen sensors:
   • Use an O2 sensor socket or wrench.
   • Disconnect the wiring harness before removal.
2. Inspect the old sensors for carbon buildup or damage.
3. Install new oxygen sensors:
   • Coat the threads of the new sensors with anti-seize compound.
   • Torque the sensors to the manufacturer's specifications (typically around 30 Nm).
4. Reconnect the wiring harness.

3. Inspect and Replace Catalytic Converter (if necessary)

1. Remove the catalytic converter:
   • Loosen the bolts or clamps securing it to the exhaust system.
   • Carefully detach it from the exhaust pipes.
2. Inspect the catalytic converter for signs of clogging or damage.
3. Install the new catalytic converter:
   • Ensure the gasket is in place and aligned correctly.
   • Secure with bolts or clamps, tightening to the manufacturer's specifications (usually around 40-50 Nm).
4. Reconnect any sensors or components removed during the process.

4. Reconnect Battery and Clear Codes

1. Reconnect the negative battery terminal.
2. Use the OBD-II scanner to clear the P0420 code from the vehicle's memory.
3. Start the engine and let it idle for a few minutes.